Automatic playing instrument



'May 24, 1927.

' 1,630,034 J. 'r. RYDBERG AUTOMATIC PLAYING INSTRUMENT Filed June 921 6 Sheets-Sheet l May 24,.1927. 1,630,034

7 J. T. RYDBERG AUTOMATIC PLAYING INSTRUMENT Fild June 18. 1921 s Sheets-Sheet 2 G no: "up

May 24, 1927.

J. T. RYDBERG AUTOMATIC PLAYING INSTRUMENT Filed June 1921 6' Sheets-Sheet 5 giij 46 :1 f WNW?" 59 f I H 15/5 Tn g A? /3 U +1 q 5 17 I fl. Z7 l 1' 7 29 r r w "j a l I if /9 I w I III PI Z I J-Mwmroz May 24.1927. 1,630,034

J. T. RYDBERG AUTOMATIC P LAYING INSTRUMENT Filed June 18. 1921 6 Sheets-Sheet 4 Fig.4. 5

I 1,630,034 May 1927' J. T. RYDBERG AUTOMATIC PLAYING INSTRUMENT Filed June 18, 1921 6 Sheets-Sheet 5 J. T. RYDBERG AUTOMATN PLAYING INSTRUMENT May 24, 1927. 1,630,034

Filed' June 18. 1921 6 Sheets-Sheet 6 O O O O O 0 i O 0 O I may Patented May 24, 1927 UNITED STATES PATENT OFFICE.

JOHN T. RYDBERG, OF BROOKLYN, NEW YORK, ASSIGNOR, BY DIRECT AND MESNE AS- SIGNMENTS, TO SUPREME PLAYER ACTION CORPORATION, A CORPORATION OF NEW JERSEY.

AUTOMATIC PLAYING INSTRUMENT.

Application filed June 18, 1921.

The present invention relates to the art of expression devices for automatic playing instruments, the'object of which is to repro duce with exactness the technique, tone, and artistic effect of a particular performer. In the conventional player piano the matter of expression is left to the operator who manually regulates the tone by means of the damper rail so that the result is perfunctorily accomplished by the operator guided by certain indicia contained upon the note sheet, but obviously the individual interpretation is far from identical at best with the actual performance of the artist. Therefore the results have been anything but satisfactory where the control as stated is left to the operator of the instrument.

This has naturally led to the devising of automatic expression control from the note sheet and tracker bar, the latter of which is provided with expression openings with which the expression perforations of the note sieet register to control certain devices affecting the operation of the player action. A large number of expression devices of this type have been heretofore proposed, as I am aware, and as to these the control is either aching in sensitiveness, on the one hand, or is accompanied by a great deal of complicacy in the mechanism on the other hand, in the latter instance adding very materially to the cost of the instrument. I

These expression devices may be said to fall into .two distinct classes: (1) Those in which the control is accomplished by means of choke valve interposed in the conduit or passage between the pumping in chanism and the wind chest whereby the operative cross-sectional area of said passage is modified withan accompanying modification of thef tension or degree of raretaction; (2) those in which this same passage is provided with a valved port regulating the admission of atmosphere with a corresponding reduction in effect of the pumping operation. Of these two, the first is the more extensively favored, but one of the main difiiculties met with, aside from'the'complicacy of the mechanism, resides in the heavy strain which is placed upon the pumping mechanism when the expression devices are so operated as'to produce the soft estdegree of modulation of the tone. On the other hand, while the Serial No. 478,691.

upon the motor is at minimum instead of at maximum under the condition recited.

Among other objects, may be enumerated that of producing a simple expression mechanism and one which is readily applicable by anyone skilled in the art to the ordinary player actions of well-known construction, either of the foot power type, motor operated, or both; of producing a mechanism of the selective type whereby the desired control may be easily selected at will and such contr 1 may pass from the extreme low to extreme high degree of modulation, or vice versa, without passing through the intermediary controls, thereby rendering the control of the different degrees of modulation substantially instantaneous.

it is further an object in View to provide control means for the wind passage in the form of *arying sized valve openings for atmosphere, each independently and sele 'tively operable to produce the particular degree of modulation and conjunctively operable for desired variations thereof.

A still further object resides in the provision of manual or automatic operating means for producing a sudden forte, some times termed crash effect.

Finally, it is further a primary object to provide suitable means fo mutlling taking of the air or eliminating the sound which is ordinarily inherent to m ratus of this type and caused by the passing of air through restricted ports or valve openings at relatively high pressure.

These and such other objects as may hereinafter appear are attained by the novel construction, combination and arrangement of partsto be hereinafter specifically described and claimed.

i of this invention.

Reference will now be had to the accompanying drawings forming a part of this specification, wherein:

Figure 1 is a front elevation of a piano player instrument having my invention applied thereto.

Figure 2 is an enlarged front elevation of my expression attachment or unit and controlling means for the player operations.

Figure 3 is a vertical sectional view taken about on the plane indicated by the line 33 of Figure 2. Y

Figure 4 is a vertical sectional view taken on the line ai t of Figure 3.

Figure 5 is a vertical sectional view taken about on the plane indicated by the line 55 of Figure 4i, and showing more particularly the crash valve feature of my apparatus.

Figure 6 is a detail plan view of a section of the key bed containing the expression control lever. V

Figure 7 is a detail view ofv the crash control button and valve.

Figure 8 is a detail view in elevation of the cut-off interposed in the passage between the tracker bar re-play opening and the controlling valve therefor.

Figure 9 is a sectional view through the cut-off of Figure 8.

Figure 10 is a diagrammatic showing of the air circuits and controlling instrumentalities of this apparatus.

Throughout the following detailed description and'on' the several figures of the drawing, similar parts are referred to by like reference characters.

Referring to the drawings, and specifically describing the invention, 1 designates a conventional type of piano player, the player action of which is designed to be op erated either by foot or motor power or mterchangeably by both. The pumping mechanism,.\\'hich does not need to be specifically referred to or described, is connected by the passage 2 to the expression unit or attachment which forms the special subject-matter This unit includes the equalizer 3, the back or stationary board 4 of which constitutes the support for subrelation thereto is attached the prunary stantially the complete mechanism of this invention.

The conduit 2 mentioned communicates with the elongated wind trunk .55, at one end thereof, best seenin Figures 3 and 1, which in turn communicates at its other end with the conduit 6 leading to the player action (not shown); Obviously, therefore, the pumping mechanism creates a suction through the passage or wind trunk 5 controlling the operation of the player action so that if the said passage is vented in any Way the degree of rarefactlon or vacuum will-be .modified and the effective operation of the player action correspondingly changed.

upon a pouch 2 f therebeneath.

In my invention, as hereinbefore premised, this passage is vented by operation of certain controlling valves which, however, are not directly actuated through the tracker bar, but indircetly, so to speak, under the control of certain pneumatics. Specifically, I provide a series of ports varying in sizes from the largest, 6, through 6 and 6 to the smallest, 6 overthe faces of which is pasted a kid strip 7 having openings registering with those mentioned, but slightly smaller in area, so as to form a flexible lip surrounding each of the openings, designed to prevent noise of the air passing through the openings when in opened condition. These openings, (5 to (3, are each provided with a valve or closure 8 carried by and forming a part ofa pneumatic 9, all of corresponding character and mounted beneath the venting ports within a housing 10 through which atmosphere is admitted to the passage 5 by way of a specially constructed entrance. Before leaving the construction it may be here stated that each of the ports 6 to 6 is provided with an adjustable slide 11 or similar means whereby the operative area of these ports may be regulated to suit the desires.

Since there is a very accelerated movement of the air into the passage 5 immediately any of its ports are opened, special attention is necessary to silence the inrush even aside from the provision of the strip 7 referred to. To this end my casing 10, or its entrance, more strictly speaking, constitutes a muffler, the passage or entrance being tortuous and completely lined throughout with felting 13 which is so applied that there exist no sharp corners at any point. The felt at the mouth of this passage is provided with a hanging and flexible lip 14 and that portion of the lining at the point 15 is so applied as to leave an air space 16 therebeneath which I find to be of considerable importance .in producing the utmost deadening of the noise. The terminals of the felting at the endof the passage 12 are also flexible'and overhanging, as indicated most clearly at 17 in Figure 3.

Beneath the wind trunk and in spaced chest 18, the tension chamber 19 of which is in open communication with the wind trunk through the passage 20 (see Figure 4). This chest contains a series of valves, each controlling the operation of the respective pneumatics 9 whose interiors are designed to be opened to the tension chamber of the primary chest when the valves are 'unseated, as will later be described. Each valve 21 is mounted upon a stem 22 which at its lower end carries a button 23 resting A tube 25 for each valve leads to the tracker bar X which is provided with suitable expression openings 101, 102, 103 and 104. WVith the normal tension in the chamber 19 the valve 21 coacts with its lower seat covering the opening or port 26, but when actuated or lifted the valve co-acts with its upper seat covering the opening 27 to atmosphere.

Thus it will be apparent that-with the valve seated on its lower seat, atmosphere passes through port 27 and passage 28 into the pneumatic 9 which is held expanded under the influence of its spring 29, but when raised to a position against its upper seat, atmosphere is cut off and the suction takes place through port 26 and passage 28, resulting in a collapse. of the pneumatic and in turn shifting the valve 8 carried thereby away from the wind trunk port with which it cooperates, allowing passage of atmos- 'phere into the said trunk and necessarily reducing the tension therein and incident thereto the effective action of the suction upon the player action. This briefly summarizes the operation of my special control which will be at a later point more greatly detailed.

It will be again noted that the atmospheric ports of this primary chest are providedwith a silencing strip 30.

Referring particularly to Figure 1, for purposes of obtaining the general control of the expression, I employ the first four valves 21 at the right of the primary chest, the one on the extreme right acting to produce the pianissimo, the next adjacent the piano,'the next the moderately loud, and the fourth the loud tone effect. The respective tubes for these valves therefore lead to the expression openings of the tracker bar which as before stated are provided in musical instruments of the typehere involved. Hence when certain expression openingsof the music sheets register with'any one or more of these openings of the tracker bar, atmosphere is admitted to actuate the particular valve or combination of these valves which is desired to produce the modulating' effect, this operation being entirely automatic under such conditions. Obviously a large range of variation is obtained by virtue of the independent and conjoined functioning of these expression valves.

, At times in the rendition of piano music it is desirable to produce what is termed a crash effect or sudden-forte, and for this purpose I have provided directly adjacent the expression valves 21 what I term the crash valve 31 which is caused to opcrate either by admission of atmosphere, through a suitable opening 105 in the tracker bar where this is provided for music out with a perforation for registry, into the tube 25 withv the result of raising the valve,

closing its atmospheric port 27 and causing the pneumatic 9 to collapse. Since the automatic operation through the tracker bar may not always be provided for, I accomplish the same result by means of a button 32 on the key bed of the piano (see Figures 7 and 10) which is arranged to open a valve 32 admitting atmosphere to the tube 25.

Vhen the pneumatic 9 collapses, as stated, as will be apparent from Figure 5 of the drawings, the rod 33 passing through the wind trunk pulls a valve 3& closed upon the entrance of the passage 35 leading from the passage 5 to the equalizer 3. Thus the equalization of pressures is prevented with the result that the tension produced by the pumping mechanism is directly effective upon the player action, causing a sudden or heavy blow of the player hammers. A further important function for this valve will appear hereafter.

There is provided in this primary a further valve 36 which is designed to be operated from the tracker bar opening 100 through the tube 25 having a cut off 49 and when said valve is unseated this permits the tension of the chamber 19 to become effective through the tube 37 leading to a loud or sustaining pedal pneumatic as shown. Additional valves may be .provided in this primary to operate bass and treble hammer rails if desired.

Passing now to the general control features of my apparatus, it will be observed that there is arranged above the wind trunk a valve box 38 also attached to the equalizer board as a part of the unit. The construction of this box is substantially the same as the primary chest below and it will sufiice to describe, therefore, merely the function ing of the valves of this box by reference to Figures 2, 4 and 10 particularly. The

first valve 39 controls the play or re-play operation. Thus when the lever 40 on the key bed is shifted toward the right the connec tion ll of its lower end pushes the movable side 42 and collapses one chamber of the double pneumatic 13. Upon the completion of the playing of the music roll, the rewind opening a of the tracker bar is uncovcred allowing atmosphere to enter through tube 14:, raising the re-wind control valve 15 next to the valve 39, and allowing the tension of the chamber 46 of this control box, which chamber it may here be stated is con nected to the wind trunk by the passage 38 as clearly shown in Figure 5, to act through the passage 4L7 upon the opposite chamber of the pneumatic 13, resulting in its collapse and shifting of the lever 40 into rewind position, the clutch mechanism (not shown) for the winding action ofthe roll being automatically thrown in for the rewinding action. Now if the notesheetis provided with a re-play perforation, it will come into registry with the tracker bar opening 6 admitting atmosphere through the passage 48, causing the valve 39 to be raised in Ion III

turn permitting the tension of the chamber 46 to become effective upon the second cham ber of the pneumatic 43 collapsing this-side thereof, and thus again throw lever over to play or re-play position, and this operation will continue so long as there is a perforation for re-playing.

In order to render the re-playing operation ineffective, I provide atone side of the spool frame a manual cut-off valve 49 which is actually arranged in the passage 48 so that in one osition this valve interrupts communication through the tube 49 and in its other position establishes such communica tion, by'virt-ue of the provision of. the passage 50 in the valve member 49 referred to.

It may here be observed that during the rewinding or rerolling of the note sheet, I make provision for cutting off communication with the player action. For this purpose as well as forother purposes, I provide in the wind trunk, as clearly shown in Figure 4, a player action cut-off valve 51 which is positioned at the entrance to the passage 6 into the wind trunk or passage 5 and normally lies in spaced relation to said passage so that the tension of the passage 5 is effective upon the player action. WVhen the lever 40 is swung into its roll re-wind position the lower end thereof impinges a spring valve member 52 uncovering the end of apassage 53 which leads to the pouch beneath the valve54 in' the valve box 38. This valve 54 is double-headed, its upper head 55 normally maintaining the chamber 46 closed against admission of atmosphere while the lower head 56 also likewise prevents admission of atmosphere into the said chamber but when the valve is raised admits the atmosphere to the passage- 57. This latter passage communicates with the pouch for the valve 51 so that upon the opening ofthe passage 53, above referred to, atmosphere causes the vali e 54 to rise allowing atmosphere to pass through 57 and causing the valve 51 to rise into position against its seat, closing off communication with the player action. Thus the valve 51 is a silencer valve. This same action of the silencer valve may be obtained by the operation of what I will term a silencer button 58 located on the key bed and designed toopen a branch passage 53' leading to the passage 53 so as to admit atmosphere in the manner above described with reference to the operation of the valve 52. The object of this manual control may be said to' be for the convenience of cutting outv sections of a particular roll which it is not desired-to playand without a discontinuance of the winding operation of said roll. Thus if after the beginning of a musical reproduction the o eratorfinds a section not to his liking, 1e 'need'only press the button 58 to discontinue the. functioning of the player action until he reaches a point of the musical note sheet which he does desire to be operative. i

I have herein described the automatic control of the expression devices through the tracker bar and'note sheet, but my invention is adapted to be manually controlled if the instrument to which it is applied is not provided with the proper tracker bar for causing said expression devices to function. To this end vI contemplate that the key bed of the instrument will be provided with a manually. operable expression lever 59 operating ina slot60 adjacent which the indicia 61 denoting the positions of the lever for tht various modulations desired is provided. This lever 59 is connected by a rod 62 to a valve member 63 pivotally mounted upon a port box 64 also forming a part of my unit. The box 64 is provided with a properly arranged series of ports 65 which communicate with the passages 25 which have heretofore been described as leading to the tracker bar. Thus the initial movement of the valve member 63 by the lever 59 will uncover the first of the ports 65, causing the operation of the proper pneumatic 9, a slightly further movement of which valve member will uncover the second of the expression ports 65, and so on. These ports are so arranged as to be completely covered by the valve member 63 under normal conditions when inoperative.

In the operation controlling device 38 there is a fourth valve designated 66 which is designed to control the switch where the player piano is electrically operated. The tube 67 for the pouch of this valve is connected to the tracker bar opening 0 so that when at the end of the note sheet the proper aperture for the purpose registers with the port 0 the valve 66 will be raised and will place the tension chamber 46 in communication through tube 67 with a switch bellows 67 of the ordinary known type and therefore not described, which bellows in turn is connected to .a switch 67 that is thrown upon the collapse of said bellows. This form of arrrangelnent of switch control is conventional.

In conclusion, I desire to revert to the construction of the equalizer 3 which is provided interiorly with a spring 68 tending to normally maintain it in expanded condition. A safety valve 69 is provided in the board 4 of this device for the purpose of preventing undue strain upon the motor. This valve is adjustable so that the tension chambers will be maintained at equalization so long as the motor for the mechanism is operated normally. In the event of abnormal or excessive tension being produced the safety valve'69 will open and this function of the valve, so far as aflecting of the tension chambers is concerned, is rendered inoperative when the crash valve 34 is closed cutting out the equalizer as hereinbefore described. It is thus that the direct effect of the motor device upon the player action is produced ,for the purpose of obtaining the crash effect. In addition to the crash function just mentioned, the crash valve 3% serves to cut off the equalizer when it is desired to produce a quick or sudden pianissimo eifect, this taking place when any one or more of the expression openings 101 to 104 are open or operative, owing to the fact that atmosphere is admitted to the tension chamber 5 immediately relieving the vacuum, which, by virtue of the closing of communication with the equalizer chamber prevents the tension therein from being equalized. Thus, owing to the relatively small capacity of the chamber 5, the effect upon the player action instead of being gradual as when the equalizer is operative, is almost immediately effective to reduce the force of operation of the player action instrumentalities. i

, Following out the functions of the equalizer which has been explained as taking care .of the equalization of pressures it should .be noted that in the normal playing opera- .tion, this equalizer is practically completely collapsed by the action of the pumping mechanism, and naturally when the expression devices are operated the pianissimo effect is produced in a gradual manner as the equalizer expands toward its maximum open .position when the tension of the spring therein is reduced.

In the reverse manner when the expression devices are employed to function toward pianoforte effect, the equalizer will be'graduallycollapsed, correspondingly increasing the tension upon the spring until the complete collapse when the effect .is very loud or FF.

It will be apparent from the foregoing that my unitary device is readily applicable to the ordinary player piano to thereby convert it into an instrument possessing the automatic expression or manual expression control. And this may be done at a minimum expense and with considerable facility because of the compactness and simplicity of my unit. In those mechanical instruments where the equalizer isapart of the mechanism Inecessarily do not have to provide this portion of the device, instead mounting my various parts upon the equalizer already a part of the equipment.

Various changes may obviously be made in other details of the construction without departing from the spirit of the invention and within the scope of the claims hereto appended.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In controlling mechanism for instru ments. of the class described having a suction device and a player action, the combination with a direct passage between the suction device and the player action having a valve port therein to admit atmosphere directly into said passage and a valve therefor normally closed, of means connected to said valve and operable by the normal tension in said passage to effect venting of the port to thereby immediately vary the effective operation of the player action.

2. In controlling mechanism for instruments of the class described having a suction device and a player action, the combi nation with a passage between the suction device and the player action, of means for variably venting said passage directly to atmosphere to immediately affect the tension in said passage and thereby modify the effective operation of the player action.

3. In expression mechanism for player instruments, the combination with air exhausting means, of a wind trunk establishing communication between the air exhausting means and the player action, having a plurality of air admission ports opening direct to atmosphere, valve means for said ports, a primary chest associated with the wind trunk, and means for operating said valve means co-operating with the primary chest and independently operable through said primary chest to uncover any one of the air admission ports and thereby vary the eifective operation of the player action through said valves.

4. In expression mechanism for player instruments, the combination with air exhausting means, of a wind trunlr establishing communication between the air exhausting means and the player action, having a plurality of air admission ports opening direct to atmosphere, valve means for said ports, a. primary chest associated with the wind trunk, and means for operating said valve means co-operating with the primary chest and independently and conjointly operable through said primary chest to uncover any one or more of the air admission ports and thereby vary the effective operation of the player action through said valves.

5. In expression mechanism for player instruments, the combination with air exhausting means, of a wind trunk establishing communication between the exhausting means and the player action having air admission ports varying in operative area and opening direct to atmosphere, valve means for said ports, operating means for said valve means including pneumatics, and means controlling actuation of said pneumat-ics from the air exhausting means to thereby variably affect the efiective operation of the player action according to the particular air admission port which is uncovered.

6. In expression mechanism for player instruments, the combination with air exhausting means, of a wind trunk establishing communication between the exhausting means and the player action having air admission ports varying in operative area, valve means for said ports, operating means for said valve means including pneumatics carrying the valve means, and means for selectively controlling actuation of said pneumatics from the air exhausting means to thereby variably affect the effective operation of the player action according to the particular air admission port which is uncovered.

7. In expression mechanism for player instruments, the combination with air exhausting means, of a wind trunk establishing communication between the exhausting means and the player action having air admission ports varying in operative area, valve means for said ports, operating means for said valve means controlled from the tracker board including pneumatics, supporting the valve means, and means for establishing communication between the pneumatics and the wind trunk to cause any of said pneumatics to uncover its air admission port to directly vent the trunk to atmosphere and thereby variably regulate the effective operation of the player action.

8. In expression mechanism for player instruments, the combination with air exhausting means, ofa wind trunk establishing communication between the exhausting means and the player action having air admission ports varying in operative area, valve means for said ports, operating means for said valve means including pneumatics, and means for selectively establishing communication between the pneumatics and the wind trunk to cause one or more of said pneumatics to uncovertheir air admission ports and thereby variably regulate the effective operation of the player action in proportion to the operative area or combined areas of the venting ports.

9. In expression mechanism for player instruments, the combination with air exhausting means,- of a tensionpassage leading to the player action and having at one side a plurality of air admission ports therein directly opening to atmosphere, valves for said ports, pneumatics for operating said valves, a passage between the pneumatics and the tension passage aforesaid, means for controlling the' operation of said pneumatics including a valve chest having a tension chamber and primary valves therein normally closing the passages leading to the pneumatics, and means for operating said primary valves to effect communication between the pneumaticsand the tension passage to produce collapse of'the pneumatics and opening of the air admission port valves.

10. In expression mechanism for player instruments, the combination with air exhausting means, of a main tension chamber leading to the player action having an air admission port, a valve therefor, means adapted to operate said valve under the influence of the tension of said main chamber, a primary chest intermediate said means and the main tension chamber controlling the valve operating means, and a tension equalizer for maintaining the equalization of the tension in the primary and main chamber.

11. In expression mechanism for player instruments, the combination with air exhausting means, of a main tension chamoer leading to the player action, expression control means and equalizer normally in open communication with the tension chamber and adapted to automatically maintain equalization of tensions during playing operation, and means for cutting off communication between the tension chamber and the equalizer to increase or decrease the efi'ective operation of the tension upon the player action, according to whether the expression control means is operative or inoperative at the time of operation of said out off means.

12. In expression mechanism for player instruments, the combination with air exhausting means, of a tension chamber connected to the player action, means for venting said chamber to effect decrease of tension in said chamber and a corresponding modification of the efiect upon the player action,

and means to suddenly increase the tension of said chamber with a corresponding increase in effective action of the air exhaust ing means upon the player action, said last mentioned means being operative to suddenly decrease the efi'ective action of the exhausting means when the venting means is operative.

13. In expression mechanism for player instruments, the combination with air exhausting means of a tension chamber, a valve for controlling admission of air to said chamber, a pneumatic for actuating said air valve, an equalizer for maintaining equalization of tensions during playing operation, valve means adapted to cut out the equalizer when it is desired to interfere with the equalization of pressures whereby to produce a crash effect, and means 0 erable to produce reversal of the effect of tlie operation of the out off valve means or sudden piano.

14. In expression mechanism for player instruments, the combination with air exhausting means, of a tension chamber, valves for variably controlling admission of air to said chamber, a pneumatic for actuating each of said air valves, an equalizer for maintaining equalization of tensions during playing operation, a valve for cutting out the'equalizer to produce from forte or piano effect according to whether the air valves are operative or inoperative, and a pneumatic for operating said valve.

15. Controlling mechanism for automatic playing instruments of the class described comprising a unitary attachment including an equalizer device, expression controlling mechanism mounted thereupon and a valve control boX also mounted upon said equalizer, each of said devices having ducts leading to the tracker bar of the instrument.

16. In expression mechanism for player instruments, the combination with air eX- hausting means, of a tension chamber having air admission ports therein, an equalizer for maintaining equalization of the tension in said chamber during playing operation, and means for rendering the equalizer inoperativewhen any air admission port is open and it is desired to interfere with the equalization of the tension whereby to produce a sudden piano or pianissimo efiect, the degree of which is controlled by the ports opened.

17. In expression mechanism for player instruments, the combination with air exhausting means, of a tension chamber having air admission ports varying in operative area, expression controlling devices operated from the tracker bar of the instrument and controlling the air admission ports aforesaid, an equalizer for maintaining equalization of the tension during playing operation, and a valve arranged intermediate the tension chamber and the equalizer and operable to render said equalizer inoperative when the air admission ports are opened under the control of the expression mechanism to thereby produce a sudden reduction in the tension with the production of a corresponding piano effect on the player action, the degree of which is proportional to the operative area of the venting port or ports.

In testimony whereof I aflix my signature.

JOHN T. RYDBERG. 

